1. Field of the Invention
The present invention relates to a light source, and more particularly to a surface light source device and a display device using the same.
2. Description of the Background Art
A conventional surface light source device has a configuration, as disclosed in Japanese Patent Publication No. 3427636, in which a conic recess is provided in order to insert a light source on a back face of a light guiding plate and a light source such as an LED is fixed to the recess. Since the recess for inserting the light source has a conic shape, a width thereof becomes narrower toward a far side from at least a leading end thereof. Therefore, the conventional surface light source device can reduce quantity of light directly emitted from the light source and produce luminous unevenness.
A surface light source device disclosed in Japanese Patent Application Laid-Open No. 10-82916(1998) has a configuration in which a light source such as an LED is pressedly inserted into a light source insertion section formed on a rear face of a light guiding plate, and a light reflection surface is formed ahead of the light source. The light reflection surface shields light emitted from the light source and directing ahead, and reflected light is guided from a side wall face of the light source insertion section into an inside of the light guiding plate, whereby luminous distribution on a light emitting surface of the light guiding plate is made uniform.
A liquid display device disclosed in Japanese Patent Application Laid-Open No. 10-104620(1998) has a configuration in which a groove for housing a cold cathode fluorescent tube is formed at a central lower part of a light guiding plate, and a light shielding quantity or reflection quantity is adjusted by a pattern or the like on a translucent adjusting film arranged on a bottom surface of the groove, whereby luminance is uniform all over a display surface and efficiency of use of the cold cathode fluorescent tube is enhanced.
However, even if the conventional surface light source device disclosed in Japanese Patent Publication No. 3427636 is used, the luminance at the conic recess becomes slightly higher than that at the other portions. Therefore, when uniform in-plane luminance is further demanded, sufficient display quality cannot be obtained from the conventional surface light source device.
When the conventional surface light source device disclosed in Japanese Patent Application Laid-Open No. 10-82916(1998) is used, direct light toward ahead of the light source is partially transmitted. Therefore, the light is not fully diffused, thereby entailing a problem that luminous unevenness is generated ahead of the light source.
Even when the conventional surface light source device disclosed in Japanese Patent Application Laid-Open No. 10-104620(1998) is used, direct light from the light source is adjusted as shielded by a pattern or the like. Therefore, the light is not fully diffused, thereby entailing a problem that luminous unevenness is generated ahead of the light source.